With the development of electronic technologies, various portable electronic apparatuses, such as cellphones, palmtop game machines, e-books and tablet computers, have been more and more frequently used in people's daily life. In some situations, a holder who carries a portable electronic apparatus may use the portable electronic apparatus while walking, for example, sending a SMS message, playing a computer game or watching video with the portable electronic apparatus while walking. In such a situation, it is very likely that the holder contact and collide with objects or other people in surrounding environment, suffering from dangers. Therefore, it is desired to have a method and a device for alerting the holder to such dangers.
A number of methods and devices for alerting holders to dangers have been proposed. For example, a portable electronic apparatus take a picture of the circumstance right ahead the holder of portable electronic apparatus with a camera built in the portable electronic apparatus and then analyzes the taken circumstance picture with a face recognition unit. When finding a face in the taken circumstance picture, the holder is alerted to danger by the portable electronic apparatus.